The present invention relates to a device for use in a wood drying kiln. More specifically, the present invention measures the moisture content at the surface of a sample of wood. The purpose of the invention is to determine the moisture content of the wood, which, when viewed in conjunction with other metrics, allows a manufacturer of lumber to determine if the lumber is adequately cured for use in wood products.
The wood drying industry, like most other industries, is progressively becoming more automated. Every industry is unique in the challenges it poses to automate the processes required for the manufacturing of products. This invention addresses one such unique automation challenge.
In order to dry wood correctly, certain parameters must be periodically monitored in a wood drying kiln. The parameters that must be monitored are humidity, temperature, and the subject of this inventionxe2x80x94wood moisture content. The first two parameters have been automated in the past as a result of technological innovations in other fields. However, the measuring of wood moisture content has been more difficult to automate.
In the past, the measuring of wood moisture content has been a strictly manual task. In order to measure wood moisture content in a kiln, an employee would need to walk into an extremely hot and humid kiln. The employee would then obtain a wood representative sample of the drying lumber. The wood sample would then be weighed. The weight of the sample of wood would be compared to established charts based on the species of the tree and the size of the sample to extrapolate the moisture content of the sample.
Once the moisture content of the sample was extrapolated, the operator of the wood drying kiln would assume that all of the wood in the kiln of the same species contained the same moisture content as the representative sample. This process is fraught with potential areas for error and economic inefficiencies. As a result, the automation of this process using more accurate technological innovations is desirable.
The undesirable aspects of the manual measuring of wood moisture content are several. First, a human being is required to enter a very acrid wood drying kiln, thereby exposing the employee to potentially hazardous fumes, including tanic acid content from the evaporating wood resins. In addition, as human beings are fallible and subject to error, it is possible that the employee in the kiln, in a hurry to exit the uncomfortable and potentially hazardous environment, might make an error in measurement, thereby jeopardizing the quality or marketability of the final product.
Second, the manufacturer must sacrifice wood samples to be measured periodically for wood moisture content, which is economically inefficient. The samples used to measure the wood moisture content would necessarily be smaller that many of the other pieces of lumber in the kiln due to the limitations of using a scale to measure the sample""s weight. The sample would need to be of a size and weight that could be easily manipulated by the employee conducting the measurements, thereby limiting its uses and sales potential once the drying process was concluded.
Lastly, the representative wood sample may not actually represent the wood moisture content of the entire batch of a particular species due to regional and individual variations in the lumber. This could result in some inaccuracies in the xe2x80x9cmeasuredxe2x80x9d wood moisture content, causing wood to be removed from the kiln too late or too early. Ultimately, removing the wood too late or too early could result in reduced market value or a reduced quality in the final product, for instance furniture or home building products.
The first efforts to automate the process of measuring wood moisture content resulted in a meter that measured the conductivity of the core of the wood sample. Two pins would be tapped into the wood at opposite ends in the geometrical center of the sample. Electrical leads would be attached to the pins and connected to an ohmmeter, allowing the manufacturer to monitor the Resistance, R, of the sample""s core. The manufacturer could thereby measure the Conductivity, YR, of the sample""s core, and correlate that conductivity with wood moisture content.
The theory behind the conductivity concept is that the presence of moisture would increase conductivity of the core of the wood. As moisture in the core of the sample decreased during the drying process, conductivity would decrease until equilibrium moisture content was reached. This process has the potential to be successful in automating the process of measuring wood moisture content, but had one significant disadvantage.
The process of tapping pins into a wood sample still resulted in the destruction of a wood sample, making the sample unfit for use in wood products. In fact, beforexe2x80x94when the manual process of measuring a wood sample was usedxe2x80x94the sample would still have some residual (albeit reduced) value because it would be undamaged and could still be sold or used in the manufacturing of wood products. Using the conductivity process, the sample with the holes resulting from the pins would be damaged and would therefore have considerably less residual value.
The present invention eliminates the need to destroy a sample, making the process of measuring wood moisture content more economically efficient.
The object of the present invention is to measure the moisture content of wood in a noninvasive manner at the surface of a typical wood sample in a kiln. In addition, the invention will be able to endure the harsh environmental conditions of a wood kiln. The invention will measure wood moisture content in the range of six percent to fifty percent moisture content. The meter will be economical, sensible, and reliable.
The aforementioned objectives can be achieved by a device in a three-stage configuration. The first stage is a capacitor with two side-by-side plates. In this configuration, with the plates applied to the wood in the drying kiln, the wood functions as a dielectric. The combination of the wood and the plates is a standard circuit capacitor.
The second stage of the invention is a circuit incorporating the wood dielectric capacitor described in the first stage. The capacitor is integrated into a xe2x80x9cone-shotxe2x80x9d CMOS LM555 clock circuit. This circuit, when activated, creates a pulse width output proportional to the capacitance of the wood.
The third stage is a microprocessor database. The database correlates the capacitance of the wood in the drying kiln with the moisture content. This is accomplished by a look-up function, which equates the width of the output pulse (and thereby the capacitance of the wood) to the wood moisture content.
The result of this three-stage invention is that the wood moisture content can be measured by using an automated, noninvasive means. The invention improves the process of measuring wood moisture content by eliminating by reducing health hazards; by reducing the potential for human error; by improving efficiency; and by making wood-drying kilns more economically competitive.